With the increasing production of shale gas and tight oils, the supply of light paraffins (e.g., C2-C8, especially C2-C5 paraffins) is increasing at an unprecedented rate in the North America region; a large fraction (up to 30%) of NGL, for example, is C4/C5 paraffins. At the same time, demand for C4/C5 molecules is decreasing due to a number of factors: 1) steam crackers switching feed from light naphtha to ethane; 2) shrinkage of gasoline pool in the North American market; and 3) a potential mandate for gasoline Reid Vapor Pressure (RVP) reduction. Although diluent use of C5s for heavy crude is predicted to grow somewhat, the supply of C4s/C5s is quickly outpacing demand and the imbalance is becoming worse with time. Profitable dispositions for ethane (e.g., cracking to make ethylene) and propane (e.g., dehydrogenation making propylene) exist. Upgrading C4/C5 paraffins to higher value and large volume products while desirable, remains challenging. Conversion of C4/C5 paraffins to heavier hydrocarbon products such as kerojet, diesel fuels as well as lube basestocks would provide a large volume and higher value outlet to help alleviate the excess of light ends in the North American market but there is no current commercial process directly converting light paraffins to heavier hydrocarbons such as these. Conventional upgrading practices typically first convert light paraffins to olefins via cracking or dehydrogenation, followed by olefin chemistries such as oligomerization or polymerization, alkylation, etc. to build higher molecular weight molecules.
A number of technologies are known to convert light paraffins to aromatics such as BTX (benzene, toluene, and xylenes). Examples of such technologies include the Cyclar™ process developed by UOP and the M2-Foming developed by Mobil Oil Corporation.
Dehydrogenation of light paraffins such as propane and iso-butane is commercially practiced; and the processes are designed to isolate high purity olefins as the final product. Current state-of-the-art processes use either Pt-based catalyst (e.g., UOP Oleflex™) or Cr-based catalyst (Houdry Catofin™ licensed by CB&I). Due to thermodynamic limitations, high temperature (>500° C.) and low pressure (vacuum or dilution with steam) are needed in order to favor the dehydrogenation reaction. Consequently, the catalyst deactivates quickly and frequent regeneration (oxychlorination for Pt-based catalysts; air burn for Cr-based catalysts) is necessary.
A number of patent publications from Nierlich et al. describe processes for converting butane to unsaturated products which could then be further reacted to produce industrially useful materials. U.S. Pat. No. 5,864,052 describes a process for preparing di-n-butene and alkyl tert-butyl ethers from field butanes by dehydrogenation and oligomerization. U.S. Pat. No. 5,994,601 describes a process for preparing butene oligomers from Fischer-Tropsh olefins by oligomerization to form dibutene. U.S. Pat. No. 5,998,685 describes the synthesis of butene oligomers by dehydrogenation of field butanes and oligomerization over a nickel-containing material such as alumina or montmorillonite. US 2002/0026087 utilizes a similar dehydrogenation/oligomerization route, again using a nickel based catalyst.
Bhasin et al, Dehydrogenation and oxydehydrogenation of paraffins to olefins, Applied Catalysts A: General 221 (2001) 397-419, provide an overview of processes for the production of olefins from paraffins by dehydrogenation and oxidative dehydrogenation.
The principle of balancing heat requirement for successive reactions is utilized in the Uhde STAR Process® for light olefin production which converts a C3/C4 paraffin feed (with recycle) in a strongly endothermic dehydrogenation reaction at 500-600° C. and 6-9 bar over a noble metal/zinc catalyst impregnated on calcium aluminate support. Part of the hydrogen from the intermediate reaction product leaving the reformer is reacted selectively with oxygen or oxygen-enriched air in an adiabatic catalytic oxy-reactor to form steam, followed by further dehydrogenation of unconverted paraffin over the same catalyst. Internally supplied heat from the exothermic hydrogen conversion reduces the external heat required for the endothermic dehydrogenation.